Self defence, although I don't think 'They hit me first' means it's self defence. 'They were going to hit me' is self defence. 'They hit me first' is revenge/just going to continue the scuffle into a fight.
Basically, I only think it's right to hit someone if you need to immediately stop what they're doing. This isn't just if you're being attacked, it can also be to stop someone from doing something that will bring harm to themselves, e.g. slapping a child's hand from an open fire.
And although I couldn't blame someone for socking someone in the face for generally being a dickhead to them, there are usually far more effective ways to deal with it that aren't going to result in you being the one who gets into trouble.
Basically, I only think it's right to hit someone if you need to immediately stop what they're doing. This isn't just if you're being attacked, it can also be to stop someone from doing something that will bring harm to themselves, e.g. slapping a child's hand from an open fire.
And although I couldn't blame someone for socking someone in the face for generally being a dickhead to them, there are usually far more effective ways to deal with it that aren't going to result in you being the one who gets into trouble.